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| United States Patent |
5,216,535
|
|
Fellows
|
June 1, 1993
|
Optical deflection device
Abstract
An optical deflection device for redirecting and/or focusing a high-power
collimated beam of light, comprising an optically transparent gas-filled
hollow sphere, and a plurality of gas-filled lenses positioned within the
sphere. When photorefractive or optically non-linear gases are used within
the sphere and lenses, a second beam of light made to travel along the
path of the original beam, will result in a local change of refractive
index of the gas, thereby altering the path of the original beam. In
separate embodiments thereof, the lenses may be mechanically repositioned,
the internal pressure of the sphere varied, or a combination of these and
the foregoing accomplished.
| Inventors:
|
Fellows; William G. (8610 Snowden Loop, Laurel, MD 20708)
|
| Appl. No.:
|
718321 |
| Filed:
|
June 17, 1991 |
| Current U.S. Class: |
359/245; 356/432; 359/299; 359/667 |
| Intern'l Class: |
G02F 001/03; G02F 001/29; G02B 001/06; G01N 021/84 |
| Field of Search: |
359/299,321-322,245,196,667,664
356/432,134
|
References Cited
U.S. Patent Documents
| 4099879 | Jul., 1978 | Britz | 359/667.
|
| 4233571 | Nov., 1980 | Wang et al. | 372/99.
|
| 4331388 | May., 1982 | McCrobie et al. | 359/667.
|
| 4402574 | Sep., 1983 | McConnel | 359/667.
|
| 4512639 | Apr., 1985 | Roberts et al. | 359/667.
|
| 4582398 | Apr., 1986 | Roberts et al. | 359/667.
|
| 4585301 | Apr., 1986 | Bialkowski | 359/243.
|
| 4714902 | Dec., 1987 | Rokni et al. | 359/299.
|
| 4740062 | Apr., 1988 | Rodriguez | 359/667.
|
| 4758072 | Jul., 1988 | Harrigan | 359/667.
|
| 4869578 | Sep., 1989 | Fukuda | 359/300.
|
| 4869579 | Sep., 1989 | Fischer | 359/299.
|
| 4940333 | Jul., 1990 | Pawliszyn | 356/432.
|
Primary Examiner: Arnold; Bruce Y.
Assistant Examiner: Lester; Evelyn A.
Attorney, Agent or Firm: Elbaum; Saul, Shapiro; Jason M.
Goverment Interests
GOVERNMENTAL INTEREST
The invention described herein may be manufactured, used and licensed by or
for the U.S. Government for governmental purposes without the payment to
us of any royalties thereon.
Claims
I claim:
1. An optical deflection device comprising:
means for providing a collimated optical beam;
a hollow optically transparent sphere in the path of said beam, wherein
said sphere contains an optically transparent gas, said gas having a
refractive index related to the pressure under which it is contained, and
said sphere being positioned in the path of said beam;
a plurality of hollow lenses, wherein said lenses are positioned within
said sphere and are filled with an optically transparent gas having a
refractive index related to the pressure under which it is contained;
whereby a predetermined deflection of said beam may be produced by altering
the position of said sphere within the path of said beam.
2. The invention of claim 1 wherein:
said gas is photorefractive;
means are provided for directing a first optical beam into said sphere;
means are provided for directing a second optical beam of selectively
variable intensity along the same path in said sphere, whereby the path of
the first optical beam varies in response to the intensity of the second
optical beam as it passes through the sphere as a result of local changes
in refractive index.
3. The invention of claim 1 wherein:
said gas is optically non-linear;
means are provided for directing a first optical beam into said sphere;
means are provided for directing a second optical beam of selectively
variable intensity along the same path in said sphere, whereby the path of
the first optical beam varies in response to the intensity of the second
optical beam as it passes through the sphere as a result of changes in
refractive index associated with stimulated Brillouin scattering.
4. The invention of claim 3 wherein said non-linear gas is methane.
5. The invention of claims 1, 2, 3, or 4 further comprising:
means for rotating said lenses within the sphere;
whereby variable deflection of the first beam may be produced without
varying the intensity of the second beam, or larger deflections may be
produced through variation of both the position of said lenses and the
intensity of the second beam.
6. The invention of claims 1, 2, 3, or 4 further comprising:
means for varying the pressure of said gas within the spherical housing;
whereby variable deflection of the first beam may be produced without
varying the intensity of the second beam, or larger deflections may be
produced through variation of both the pressure of said gas within the
sphere and the intensity of the second beam.
7. The invention of claims 1, 2, 3, or 4 further comprising:
means for rotating the lenses within said sphere;
means for varying the pressure of said gas within the spherical housing;
whereby variable deflection of the first beam may be produced without
varying the intensity of the second beam, or larger deflections may be
produced through variation of the pressure of said gas, the position of
said lenses, and the intensity of the second beam.
8. A method for steering an optical beam, said method comprising:
(a) directing a first beam into a gas-filled hollow sphere;
(b) transmitting said beam through a plurality of gas-filled convex lenses
within said sphere, said lenses being connected to means for rotation
within said sphere;
(c) outputting said beam from the sphere;
(d) monitoring the reflected intensity of said beam with photodetectors;
and
(e) moving said convex lenses to control the deflection of said beam.
9. A method for steering an optical beam, said method comprising:
(a) directing a first beam into a gas-filled hollow sphere, said sphere
having means for varying the internal pressure of said gas;
(b) transmitting said beam through a plurality of gas-filled convex lenses
within said sphere;
(c) outputting said beam from the sphere;
(d) monitoring the reflected intensity of said beam with photodetectors;
and
(e) varying the internal pressure of said sphere to control the deflection
of said beam.
10. A method for steering an optical beam, said method comprising:
(a) directing a first beam of low intensity into a gas-filled hollow
sphere, said sphere having means for varying the internal pressure of said
gas;
(b) transmitting said beam through a plurality of gas-filled convex lenses
within said sphere;
(c) outputting said beam from the sphere;
(d) monitoring the reflected intensity of said beam with photodetectors;
and
(e) moving said convex lenses to control the deflection of said beam.
(f) directing a second beam of high intensity into said gas-filled hollow
sphere;
(g) transmitting said second beam through a plurality of gas-filled convex
lenses within said sphere;
(h) outputting said second beam from the sphere and onto said target.
11. A method for steering an optical beam, said method comprising:
(a) directing a first beam of low intensity into a gas-filled hollow
sphere;
(b) transmitting said beam through a plurality of gas-filled convex lenses
within said sphere, said lenses being connected to means for rotation
within said sphere;
(c) outputting said beam from the sphere;
(d) monitoring the reflected intensity of said beam with photodetectors;
and
(e) moving said convex lenses to control the deflection of said beam.
(f) directing a second beam of high intensity into said gas-filled hollow
sphere;
(g) transmitting said second beam through a plurality of gas-filled convex
lenses within said sphere;
(h) outputting said second beam from the sphere and onto said target.
12. The invention of claims 8, 9, 10 or 11 wherein said gas is
photorefractive.
13. The invention of claims 8, 9, 10 or 11 wherein said gas is optically
non-linear.
14. The invention of claims 8, 9, 10 or 11 wherein said gas is methane.
Description
BACKGROUND OF THE INVENTION
Most conventional optical deflection devices involve the use of optically
flat mirrors, either alone or in combination. An advantage to using this
type of mirror, as opposed to crystalline or reflective lenses, is that a
collimated beam of light can be redirected without significant divergence
or focusing. This becomes important in applications where the deflected
beam must be detectable at great distances.
A typical mirror is formed by depositing a reflective coating, such as
gold, upon an optically flat substrate. These surfaces, however, can be
seriously degraded, or even vaporized by a sufficiently powerful optical
signal. Laser-based communications networks or weapon systems positioned
in space could employ such high energy laser beams.
As an alternative to mirrors, it is possible to use transparent optical
flats to deflect a beam of light. If a glass or quartz flat is oriented at
an oblique angle to an incoming beam of light, a controlled deflection
will result owing to the increased refractive index of the glass or
quartz. Unfortunately, crystalline flats used in this way will produce
little deflection, and because their refractive indices are fixed, the
deflection may only be controlled by mechanically repositioning the flat.
Most electronic and electro-optic beam steering techniques are based on the
use of periodic changes in a crystal's refractive index due to
acousto-optic or photorefractive effects. See Sincerbox, G. T., Roosen,
G., "Opto-optical Light Deflection," Applied Optics, Vol. 22, No. 5, 690
(1983). Thus, Fischer, et. al., U.S. Pat. No. 4,869,579, teaches the use
of a third order nonlinear crystal such as BaTiO.sub.3, together with two
incident pumping beams differing in either phase or frequency, to create a
periodic variation of refractive index, or index grating, such that the
beams are diffracted at a controllable angle.
Thermal effects were used by Bialkowski, U.S. Pat. No. 4,585,301, to create
an optical switch within a photorefractive material. A control beam
passing through the medium sets up a thermal lens or gradient. A second
beam is deflected by the "lens" to a prepositioned detector. The invention
does not rely on the change in refractive index at the interface of an
on-linear material, nor is it limited to a localized change in the
refractive index (i.e. not making use of reflection). For this reason,
Bialkowski suggests the use of FREON 12 as an absorbing gas to create the
thermal gradient, and argon as an inert gas for mixing.
When non-linear optical gases have been used, it has mainly been to produce
phase conjugate replicas of an incident beam, typically in reflection. See
Fukuda, U.S. Pat. No. 4,869,578; Wang et al., U.S. Pat. No. 4,233,571.
Fukuda teaches a gas-dynamic phase-conjugated mirror, and notes that
non-linear gases, as opposed to non-linear liquids or solids, can
withstand very hig light intensities (>2.times.10.sup.9 W/cm.sup.2). For
this reason, phase conjugating mirrors have found use in laser fusion
applications.
In situations where it is desirable to focus a laser beam on targets at
great distances in space, it is necessary to use focusing optics with very
large output apertures (up to 5 meters in diameter) and near diffraction
limited performance. Crystalline lenses of this size are difficult to
produce with good optical quality, and may be too heavy to boost into
space. Additionally, a crystalline lens is limited to but one focal length
as a consequence of its shape and refractive index.
Roberts and Honeycutt, U.S. Pat. No. 4,512,639 (1985), teaches an erectable
large optic for outer space applications utilizing a gas dynamic lens of
fixed focal length. Jets of gas having a refractive index, n, are used to
deflect and focus a diverging laser source. As the gas disperses, the
refractive index of the gas decreases so that the index varies from the
outer boundary of the lens to its inner boundary. Nitrogen, helium, and
oxygen are listed as possible gases for this use.
To overcome focal length limitations, Roberts and Honeycutt, U.S. Pat. No.
4,582,398 (1986), suggests the use of a large continuously focusable gas
lens. Essentially a large balloon, it is fabricated from a material such
as chloride/vinylidene chloride copolymer (Saran wrap), and is inflated
using gas dynamic nozzles. To alter the focal length of the balloon it is
mechanically deformed, making changes in deflection slow and inaccurate.
A gas zoom lens is described by McCrobie et al., U.S. Pat. No. 4,331,388
(1982) for use with a camera. A plurality of conventional lenses are
positioned around a central cavity which is filled with an optically
transparent gas such as FREON. By altering the cavity pressure the
refractive index of the gas is changed, thereby allowing variable focal
lengths. This magnification system, however, is of little use as a beam
steerer or deflector. In space-based applications, for example, the
crystalline optics would prove too heavy, and their fabrication too
costly.
Accordingly, it is an object of the present invention to provide an optical
deflection device comprising only gas-filled optics to achieve high
optical quality, low attenuation, light weight construction, and the
ability to withstand very intense beams of light.
It is another object of the present invention to provide an optical
deflection device comprising only gas-filled optics, which allows rapid
variation of a beam's direction through the use of photorefractive gases,
which upon optical stimulation experience a change in refractive index and
affect the path of a second beam of light.
It is still another object of the present invention to provide an optical
deflection device comprising only gas-filled optics, which allows rapid
variation of a beam's direction through the use of optically non-linear
gases, which upon optical stimulation set up stimulated Brillouin
scattering, which in turn causes acoustic waves to be generated by
electrostriction. As a result, the density, and therefore the refractive
index, of the non-linear medium is modified in response to the optical
signal, and the path of a second optical beam may be altered.
It is also an object of the present invention to provide an optical
deflection device comprising only gas-filled optics, which in addition to
having means for opto-optical deflection, is provided with means to either
mechanically position the gas lenses, or to alter the pressure of the gas
in at least one of the lenses.
SUMMARY OF THE INVENTION
The present invention relates to an optical deflection device for
redirecting and/or focusing a high-power beam of light. A hollow optically
transparent sphere is filled with an optically transparent gas having a
refractive index related to the pressure within the sphere. Two or more
hollow lenses are positioned within the sphere, and are filled with an
optically transparent gas having a refractive index related to the
pressure within the lens. If a collimated beam of light is made to pass
through the gas-filled sphere and lenses, it will be deflected and/or
focused in accordance with Snell's Law and geometric optics.
The present invention additionally provides for the hollow sphere and
lenses to be filled with a photorefractive gas, such that when means are
provided for directing a second beam of light through the gas-filled
optics, the path of the original beam will be altered in response to the
second.
The present invention further provides for the hollow sphere and lenses to
be filled with an optically non-linear gas, such as methane, such that
when means are provided for directing a second beam of light through the
gas-filled optics, stimulated Brillouin scattering will be produced along
with a concomitant change in refractive index, thereby altering the path
of the original beam in response to the second.
The present invention also provides, in addition to the foregoing, means
for rotating the gas-filled lenses and/or to regulate the internal
pressure of the hollow sphere. Thereby producing greater deflections or
alternate means of deflection.
The present invention further provides a method for steering an optical
beam, comprising directing a first beam such that it intercepts the
sphere, transmitting the beam through a plurality of gas-filled lenses
within the sphere, outputting the beam from the sphere, monitoring the
reflected intensity of the beam with photodetectors, and moving the convex
lenses through mechanical means to control the deflection of the beam.
The present invention also provides a method for steering an optical beam,
comprising the foregoing steps, but varying the internal pressure of the
sphere to control the deflection of the beam, rather than moving the
convex lenses.
The present invention additionally provides a method for steering an
optical beam, wherein the optics are filled with a photorefractive gas,
and means are provided for directing a second beam of light through the
sphere, thereby altering the path of the first.
The present invention further provides a method for steering an optical
beam, wherein the optics are filled with an optically non-linear gas, and
means are provided for directing a second beam of light through the
sphere, thereby altering the path of the first.
It is an aspect of this invention to provide a hollow lens filled with an
optically non-linear gas, such as methane. The hollow lens may be
fabricated from an optically transparent, rigid material, such as quartz,
and may be double convex.
BRIEF DESCRIPTION OF THE DRAWINGS
The preferred embodiments of the present invention will be described with
reference to the accompanying drawings.
FIG. 1 is a cross-sectional view of the optical deflection device using
static lenses and linear gases.
FIG. 2 is a cross-sectional view of the optical deflection device using
static lenses and either photorefractive or optically non-linear gases.
FIG. 3 is a cross-sectional view of the optical deflection device with
means to position the lenses.
FIG. 4 is a cross-sectional view of the optical deflection device with
means for altering the internal pressure of the sphere.
FIG. 5 is a cross-sectional view of the optical deflection device with
means to position the lenses and to alter the internal pressure of the
sphere.
FIG. 6 is a schematic diagram of a method for controlling the deflection of
an optical beam.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 illustrates an embodiment of the optical deflection device employing
no moving parts. The deflection of an incoming beam of light (the signal)
11, is controlled by positioning the optical deflection device as if it
were a lens or mirror of fixed focal length. The beam 11 intercepts an
optically transparent spherical housing 13, passes through one of a
plurality of gas-filled lenses 15, through the gas-filled interior of the
sphere 13 and other lenses 15, and emerges as a redirected and/or focused
beam.
The housing 13 and lenses 15 may be flexible or rigid depending on the
application. In space, where payload size and weight must be minimized, an
inflatable plastic housing may be desirable. In the laboratory, or in
laser-based machining processes, rigid materials would suffice. Suitable
housing and lens materials include, but are not limited to quartz, optical
quality glasses such as NESA, and rigid plastics. The wall thicknesses
should be such that within the range of operating pressures the
deformation of the housing and lenses is wholly elastic (i.e. able to be
calculated), and the beam deflection is minimized within the wall itself.
The lenses 15 may be double convex, single convex, flat, double concave,
single concave, or any other shape depending on the application. In
addition, all of the lenses 15 need not be the same shape, particularly
where collimation is desired and the sphere is not large enough to
accommodate two lenses of the same focal length.
The actual deflection of the incident beam can be calculated using Snell's
law, which is written:
n.sub.o sin.alpha.=nsin.beta.
where n.sub.o is the refractive index of the first medium, .alpha.is the
angle of incidence relative the axis normal to the interface, n is the
refractive index of the second medium, and .beta. is the angle of
emergence into the second medium. If the wall thickness of the housing is
kept to a minimum, the majority of the deflection will occur in the gas
medium within the housing 13 and lenses 15.
At a given temperature the refractive index of the gas 17 is directly
proportional to its density, and therefore to its pressure. By filling the
housing 13 and lenses 15 with optically transparent gases at a
predetermined pressure it is possible to fix the refractive index of each
of these optical components. The gas pressure within the lenses 15 need
not be the same as that within the sphere. In fact, were it the same, the
lenses would serve little purpose in this embodiment. Suitable gases
include N.sub.2, H.sub.2, O.sub.2, A, and Ne among others.
In a second embodiment, illustrated in FIG. 2, the aforementioned housing
13 and lenses 15 are filled with a photorefractive gas 17, such as Freon
12. When a second beam of light (the control beam) 19, is transmitted into
the photorefractive medium 17, a local change in the refractive index of
the medium is accomplished through either thermal absorption,
spectroscopic transitions, or photochemical processes, depending on the
gas. The path of the signal beam 11 is thereby altered in response to the
presence of the control beam 19. The intensity of the control beam 19 can
be altered to control the refractive index of the medium 17 in a
predetermined manner. The control beam 19 may be of a different wavelength
than the signal beam 11, and may be either pulsed or continuous.
In another embodiment, the housing 13 and lenses 15 are filled with an
optically non-linear gas 17 such as CH.sub.4. Other suitable gases
include, but are not limited to, Xe, C.sub.2 F.sub.6, CClF.sub.3, or
SF.sub.4. A non-linear gas is also one whose refractive index changes in
response to the intensity of an incident beam of light. However, the
mechanism by which this occurs is photoacoustic, and comes about as a
result of stimulated Brillouin scattering within the medium. Above certain
threshold pressures non-linear gases may act as a "mirror", and actually
reflect the phase conjugate of an incident beam.
It is an object of the present invention, however, to operate at pressures
below the phase conjugation threshold (100 atmospheres for CH.sub.4), so
that the signal beam 11 may be transmitted without appreciable loss due to
reflection. This, in addition to the fact that non-linear gases can
withstand very high light intensities (>2.times.10.sup.9 W/cm.sup.2), make
non-linear gases a good choice for opto-optical deflection.
In another embodiment, illustrated in FIG. 3, mechanical means 21, 23, 24
are provided for positioning the lenses 15 in relation to the signal beam
11, thereby providing an independent or additional means for controlling
deflection. In a possible configuration, the lenses 15 are mounted on
rails 21, which may be moved by gears 23, driven by a servo-motor 24.
Other possibilities include spring loaded mechanisms, hydraulic actuators,
piezo-electric devices, or other means known to those skilled in the art.
FIG. 4 illustrates the use of a pressure valve 25 and gas source 27 to
alter the pressure of the gas contained within the spherical housing 13.
Another possible means of controlling the pressure would be to employ
heaters. As mentioned previously, the pressure of a gas is directly
proportional to its refractive index. Thus, by increasing or decreasing
the pressure of the gas, it is possible to control the deflection of the
signal beam 11 either independently or in conjunction with other means
(see FIG. 5).
If the optical deflection device is used to steer a beam in machining
processes as illustrated in FIG. 6, where the target 29 is accessible, it
is possible to position one or more photodetectors 31 to monitor the
reflected intensity. This information can then be processed as part of an
external feedback loop 33 which would alter the intensity of the control
beam 19, the position of the lenses 15, and/or the gas pressure within the
spherical housing 13 to adjust the deflection of the beam 11. Since, in
most applications the light intensity will be strong, photodiodes and
photoresistors are possible detectors.
Where precise machining is desired, an aiming process for directing the
deflected laser light can be achieved by employing either a dual laser
system having a low intensity pointing beam 19 and a high intensity
cutting beam 11, or a single beam having dual intensities. The aiming beam
11 is first passed through the optical deflection device and its position
on the target 29 monitored using photodetectors 31. The position of the
aiming beam 11 is fed back to the control system 33, which in turn adjusts
the position of the beam 11 more precisely. When the desired position is
achieved, the higher energy laser beam 11 is transmitted through the
optical deflection device and onto the target 29.
While there has been described and illustrated specific embodiments of the
invention, it will be obvious that various changes, modifications, and
additions, can be made herein without departing from the field of the
invention which should be limited only by the scope of the appended
claims.
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